This invention relates to oxide-based materials that have one application as phosphors. More particularly, the phosphors are aluminates or borates doped with Pr3+ and exhibit quantum splitting when irradiated with vacuum ultraviolet (“VUV”) radiation. This invention also relates to a method of making such quantum-splitting phosphors.
The conversion of a single ultraviolet (“UV”) photon into two visible photons with the result that the quantum efficiency of luminescence exceeds unity is termed quantum splitting. Quantum splitting materials are very desirable for use as phosphors for lighting applications, such as fluorescent lamps. A suitable quantum splitting phosphor can, in principle, produce a significantly brighter fluorescent light source due to higher overall luminous output because it can convert to visible light the part of UV radiation that is not absorbed efficiently by traditional phosphors currently used in commercial fluorescent lamps. Quantum splitting has been demonstrated previously in fluoride- and oxide-based materials. A material comprising 0.1% Pr3+ in a matrix of YF3 has been shown to generate more than one visible photon for every absorbed UV photon when excited with radiation having a wavelength of 185 nm. The measured quantum efficiency of this material was 140%, and thus greatly exceeded unity. However, some fluoride-based compounds in the art do not have sufficient stability to permit their use as phosphors in fluorescent lamps because they are known to react with mercury vapor that is used in such lamps to provide the UV radiation and form materials that do not exhibit quantum splitting. Other fluoride-based phosphors require the use of relatively expensive materials. In addition, producing fluoride-based materials presents a great practical challenge because it may involve the use of large quantities of highly reactive and toxic fluorine-based materials.
Therefore, there is a continued need to provide quantum-splitting phosphors that have higher quantum efficiency in the visible range than the prior-art quantum splitting materials. It is also desirable to provide more energy-efficient light sources using quantum-splitting phosphors having higher quantum efficiency. It is further desirable to provide simple methods for making materials having high quantum-splitting capability.